Imported media relies on GUID for download

[pathartl]

When importing media with the importer plugin, the GUID is used as the URL for downloading the files. If there is more than two levels of sites you're importing between this creates an issue with flow.

In example, say you have three sites:
​http://siteone.com (Original WP install)
​http://sitetwo.com
​http://sitethree.com

Exporting from ​http://siteone.com and importing on ​http://sitetwo.com the files will be downloaded from ​http://siteone.com.

However, if you export from ​http://sitetwo.com and import into ​http://sitethree.com, without changing the GUID, the files will be downloaded from ​http://siteone.com

In most cases ​http://siteone.com would be nonexistent or unreachable at this point, thus the media items cannot be imported.

Note that wp_get_attachment_url had this same defect (7622)

[DrewAPicture]

This seems like expected behavior to me. The guid is meant to persist with the attachment post data, which means that if you moved the content twice, the original guid would persist as expected.

[dd32]

Although this might be the expected behaviour of the exporter/importer, it's most definately an incorrect assumption.

We shouldn't be relying upon the GUID for anything other than "This is item X", it should never be treated as a permanent URL.